1. Technical Field of the Invention
The present invention relates generally to an improved structure of a fuel injector capable of adjusting fuel jet characteristics such as the quantity of a fuel jetting out of the fuel injector and fuel injection time lag after assembled.
2. Background Art
Fuel injectors are known in the art which are designed to control the fuel pressure in a pressure chamber formed in a nozzle body which acts on a valve for closing an injection nozzle. For moving the valve, the fuel injector controls a balance of a valve-opening pressure developed by the fuel pressure supplied to a fuel sump, a valve-closing pressure developed by the fuel pressure in the pressure chamber, and a spring pressure acting on the valve to close the nozzle. Within the pressure chamber, a fuel drain valve is installed. The regulation of the fuel pressure in the pressure chamber is accomplished by opening and closing the fuel drain valve.
Japanese Patent No. 2599281 discloses such a fuel injector which is illustrated in FIG. 8.
A constant pressure of fuel is supplied to a pressure control chamber 211 and a fuel sump 216. A valve hole 207 leading to the pressure chamber 211 is closed by a control valve 206. When the sum of the fuel pressure in the control pressure chamber 211 working to urge the control valve 206 in a valve-opening direction and the attractive force produced by an electromagnet 213 attracting an armature 205 overcomes the spring pressure of a coil spring 203 urging the control valve 206 in a valve-closing direction, it will cause the control valve 206 to be lifted up to open the valve hole 207, so that the fuel pressure in the control pressure chamber 211 drains to a magnet chamber 215 through a valve chamber 217 and holes formed in a yoke 212, thereby resulting in a drop in fuel pressure within the control pressure chamber 211. This causes the sum of fuel pressure in the fuel sump 216 urging a nozzle valve 200 in a spray hole-opening direction and the pressure produced by a coil spring 218 urging the nozzle valve 200 in a spray hole-closing direction to overcome the fuel pressure in the control pressure chamber 211, thereby lifting the nozzle valve 200 upward. When the electromagnet 213 is deenergized, it will cause the control valve 206 to close the valve hole 207, thereby resulting in an increase in fuel pressure within the control pressure chamber 211. This causes the nozzle valve 200 to be moved downward to close the spray hole. The injection timing, therefore, has a correlation with the time of lift of the control valve 206. The quantity of fuel injected has a correlation with the length of time the valve hole 207 is opened.
The above fuel injector, however, has a problem that it is difficult to adjust the quantity of fuel injected after the fuel injector is assembled. The reason for this will be discussed below.
The lift of the control valve 206 undergoes a time lag between application of a drive pulse signal to the electromagnet 213 and action of a valve-lifting force on the control valve 206. The injection delay depends upon the spring load produced by the spring 203 on the control valve 206 in the valve-closing direction. The spring load is determined by the degree to which an adjusting screw 202 is fastened. It is, however, impossible to change the fastening degree of the adjusting screw 202 after the fuel injector is assembled, thus resulting in a difficulty in adjusting the time lag and the action of the valve-lifting force on the control valve 206.
If the width of the drive pulse signal applied to the electromagnet 213 is constant, and the fuel pressure supplied to the fuel injector is also constant, the opening duration of the valve hole 207 depends upon a time delay between rising of the drive pulse signal and the time the control valve starts to be lifted and a time delay between falling of the drive pulse signal and the time the control valve closes the valve hole 207. The valve lift time delay depends upon the spring load of the spring 203 and, thus, impossible to regulate after the fuel injector is assembled. The valve closing time delay depends upon the amount of lift of the control valve 206 and the spring load of the spring 203. A maximum amount of lift of the control valve 206 is determined by an air gap between the stator or yoke 204 and the armature 205. It is, however, impossible to adjust the spring load for the same reason as described above. The electromagnet 213 and the valve hole 207 are both restrained by a guide member 208 from moving. The guide member 208 is held between a nozzle body 209 and a control body 214. The air gap between the yoke 204 and the armature 205 is a function of the distance between the valve hole 207 and the yoke 204. It is, thus, impossible to change the amount of lift of the control valve 206 after the fuel injector is assembled. For these reasons, the opening duration of the valve hole 207 cannot be adjusted after the assembly of the fuel injector, thus resulting in a difficulty in regulating the quantity of fuel to be injected into the engine.
Accordingly, the regulation of the quantity of fuel injected should be accomplished by repeating a series of operations: inspection of the quantity of fuel injected, disassembly of the fuel injector, turning of the adjusting screw 202, and/or replacement of the guide member 208. This, however, results in a great reduction in productivity. It is also impossible to eliminate a difference in quantity of fuel injected between fuel injectors arising from a difference in size between spray holes.
Further, it is impossible to drain the fuel in the control pressure chamber 211 from a drain passage 201 along a longitudinal center line of the fuel injector. The fuel is, in practice, discharged to the drain passage 201 from the valve hole 207 through the magnet chamber 215 surrounding the electromagnet 213, thus resulting in an increase in size of the fuel injector in a widthwise-direction thereof.
It is therefore a principal object of the invention to avoid the disadvantages of the prior art.
It is another object of the invention to provide a compact structure of a fuel injector which is capable of adjusting a fuel jet characteristic such as the quantity of a fuel jet to a target one after the fuel injector is assembled.
According to one aspect of the invention, there is provided an improved structure of a fuel injector capable of adjusting a fuel jet characteristic after assembled. The fuel injector comprises: (a) a nozzle having formed therein a spray hole from which fuel is sprayed; (b) a nozzle valve selectively opening and closing the spray hole; (c) an injector body supporting therein the nozzle valve slidably, the injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in the injector body to produce fuel pressure urging the nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging the nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in the injector body; (d) a control valve selectively opening and closing the valve hole formed in the injector body; (e) a first urging mechanism urging the control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; (f) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil, the movable portion including an armature which is connected fixedly to the control valve and spaced from the stator through a given air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move the control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port; (g) a second urging mechanism urging the stationary portion of the control valve moving mechanism in a first direction identical with the valve hole-opening direction; and (h) an air gap adjusting member disposed around the stationary portion of the control valve moving mechanism in engagement with the injector body so as to urge the stationary portion of the control valve moving mechanism in a second direction opposite the first direction against an urging pressure produced by the second urging mechanism to keep the air gap between the stator and the armature, the air gap adjusting member being designed to be movable selectively in the first direction and second direction for changing the air gap.
In the preferred mode of the invention, the air gap adjusting mechanism is connected to the injector body in a screw fashion. For example, the air gap adjusting mechanism has formed therein an internal thread engaging an outer thread formed on an end portion of the injector body and forms a sliding pair with the control pair moving mechanism.
The air gap adjusting mechanism is made of a hollow member fitted on the injector body.
The second urging mechanism is implemented by a disc spring disposed within the injector body.
According to the second aspect of the invention, there is provided an improved structure of a fuel injector capable of adjusting a fuel jet characteristic after assembled. The fuel injector comprises: (a) a nozzle having formed therein a spray hole from which fuel is sprayed; (b) a nozzle valve selectively opening and closing the spray hole; (c) an injector body supporting therein the nozzle valve slidably, the injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in the injector body to produce fuel pressure urging the nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging the nozzle valve in a spray hole-closing direction, and a valve hole for establishing fluid communication between the pressure chamber and a drain port formed in the injector body; (d) a valve chamber formed in the injector body downstream of the valve hole; (e) a control valve movable within the valve chamber to selectively open and close the valve hole formed in the injector body, when leaving the valve hole, the control valve defining in the valve chamber a first drain passage communicating with the pressure chamber through the valve hole; (f) an urging mechanism disposed within an urging mechanism mount chamber formed in the injector body leading to the first drain passage, the urging mechanism working to produce an urging pressure which urges the control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the valve chamber; (g) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil, the movable portion including an armature which is connected fixedly to the control valve, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move the control valve in a valve hole-opening direction against the urging pressure produced by the urging mechanism, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the first drain passage; and (h) an urging pressure adjusting mechanism disposed within the injector body in contact with the urging mechanism, the urging pressure adjusting mechanism being so designed as to be movable in engagement with an inner wall of the urging mechanism mount chamber for changing the urging pressure produced by the urging mechanism, the urging pressure adjusting mechanism having formed therein a second drain passage communicating between the first drain passage and the drain port through the urging mechanism mount chamber.
In the preferred mode of the invention, the urging pressure adjusting mechanism engages the inner wall of the urging mechanism mount chamber in a screw fashion.
The urging pressure adjusting mechanism may alternatively be press-fitted within the urging mechanism mount chamber.
The fuel injector further comprises a second urging mechanism which urges the stationary portion of the control valve moving mechanism in a first direction identical with the valve hole-opening direction and an air gap adjusting member disposed around the stationary portion of the control valve moving mechanism in engagement with the injector body so as to urge the stationary portion of the control valve moving mechanism in a second direction opposite the first direction against an urging pressure produced by the second urging mechanism to keep an air gap between the stator and the armature. The air gap adjusting member is designed to be movable selectively in the first direction and second direction for changing the air gap.
The air gap adjusting mechanism is connected to the injector body in a screw fashion.
The air gap adjusting mechanism has formed therein an internal thread engaging an outer thread formed on an end portion of the injector body and forms a sliding pair with the control pair moving mechanism.
The air gap adjusting mechanism is made of a hollow member fitted on the injector body.
The second urging mechanism is implemented by a disc spring disposed within the injector body.
According to the third aspect of the invention, there is provided a method of adjusting a fuel injection characteristic of a fuel injector which is designed to inject fuel into an engine and which includes: (a) a nozzle having formed therein a spray hole from which fuel is sprayed; (b) a nozzle valve selectively opening and closing the spray hole; (c) an injector body supporting therein the nozzle valve slidably, the injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in the injector body to produce fuel pressure urging the nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging the nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in the injector body; (d) a control valve selectively opening and closing the valve hole formed in the injector body; and (e) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil wound around the stator, the movable portion including an armature which is connected fixedly to the control valve and spaced from the stator through a given air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move the control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port so that the fuel pressure in the pressure chamber is decreased to move the nozzle valve so as to open the spray hole. The method comprises the steps of: (a) supplying a test liquid to the fuel injector from the inlet at a given pressure level higher than half a maximum pressure of the fuel which is supplied to the fuel sump and the pressure chamber when the fuel injector is actually used to inject the fuel into the engine; (b) applying a drive pulse signal to the coil of the control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole; and (c) changing the air gap between the stator and the armature to adjust a quantity of the test liquid sprayed from the spray hole to a target one.
The fuel injector further comprises: (a) a first urging mechanism urging the control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; (b) a second urging mechanism urging the stationary portion of the control valve moving mechanism in a first direction identical with the valve hole-opening direction, and (c) an air gap adjusting member disposed around the stationary portion of the control valve moving mechanism in engagement with the injector body so as to urge the stationary portion of the control valve moving mechanism in a second direction opposite the first direction against an urging pressure produced by the second urging mechanism to keep the air gap between the stator and the armature. The air gap adjusting member is designed to be movable selectively in the first direction and second direction for changing the air gap. The air gap changing step moves the air gap adjusting mechanism to change the air gap between the stator and the armature to adjust the quantity of the test liquid sprayed from the spray hole to the target one.
The drive pulse applying step applies a first drive pulse signal and a second drive pulse signal having a width different from that of the first drive pulse signal in sequence to the coil of the control valve moving mechanism to energize the coil during the air gap changing step.
The width of the first drive pulse signal is longer than that required to move the nozzle valve until a maximum rate of a jet of the test liquid from the spray hole is reached.
If target quantities of the test liquid sprayed from the spray hole when the first and second drive pulse signals are applied to the coil of the control valve moving mechanism are defined as a first and a second target value, respectively, a difference between a quantity of the test liquid sprayed from the spray hole when the first drive pulse signal is applied to the coil and the first target value is defined as xcex41, a difference between a quantity of the test liquid sprayed from the spray hole when the second drive pulse signal is applied to the coil and the second target value is defined as xcex42, the air gap changing step changes the air gap so as to meet at least one of a condition of xcex412+xcex422xe2x89xa6K1 and a condition of xcex41xc3x97xcex42 less than 0, xcex41xe2x89xa6K2, and xcex42xe2x89xa6K3 where K1, K2, and K3 are preselected target values, (e.g., 1 mm3/st, 0.5 mm3/st, and 1 mm3/st), respectively.
According to the fourth aspect of the invention, there is provided a method of adjusting a fuel injection characteristic of a fuel injector which is designed to inject fuel into an engine and which includes: (a) a nozzle having formed therein a spray hole from which fuel is sprayed; (b) a nozzle valve selectively opening and closing the spray hole; (c) an injector body supporting therein the nozzle valve slidably, the injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in the injector body to produce fuel pressure urging the nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging the nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in the injector body; (d) a control valve selectively opening and closing the valve hole formed in the injector body; (e) an urging mechanism disposed within an urging mechanism mount chamber formed in the injector body, the urging mechanism working to produce an urging pressure which urges the control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; and (f) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil wound around the stator, the movable portion including an armature which is connected fixedly to the control valve, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move the control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port so that the fuel pressure in the pressure chamber is decreased to move the nozzle valve so as to open the spray hole. The method comprises the steps of: (a) supplying a test liquid to the fuel injector from the inlet at a given pressure level higher than half a maximum pressure of the fuel which is supplied to the pressure chamber when the fuel injector is actually used to inject the fuel into the engine; (b) applying a drive pulse signal to the coil of the control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole; and (c) changing the urging pressure produced by the urging mechanism to adjust a quantity of the test liquid sprayed from the spray hole to a target one.
The fuel injector further comprises an urging pressure adjusting mechanism disposed within the injector body in contact with the urging mechanism. The urging pressure adjusting mechanism is so designed as to be movable in engagement with an inner wall of the urging mechanism mount chamber for changing the urging pressure produced by the urging mechanism. The urging pressure adjusting mechanism has formed therein a second drain passage communicating between a first drain passage communicating with the pressure chamber through the valve hole and the drain port through the urging mechanism mount chamber. The urging pressure changing step moves the urging pressure adjusting mechanism to shift the urging mechanism for adjusting the quantity of the test liquid sprayed from the spray hole to the target one.
The drive pulse applying step applies a first drive pulse signal and a second drive pulse signal having a width different from that of the first drive pulse signal in sequence to the coil of the control valve moving mechanism to energize the coil during the air gap changing step.
The width of the first drive pulse signal is longer than that required to move the nozzle valve until a maximum rate of a jet of the test liquid from the spray hole is reached.
If target quantities of the test liquid sprayed from the spray hole when the first and second drive pulse signals are applied to the coil of the control valve moving mechanism are defined as a first and a second target value, respectively, a difference between a quantity of the test liquid sprayed from the spray hole when the first drive pulse signal is applied to the coil and the first target value is defined as xcex41, a difference between a quantity of the test liquid sprayed from the spray hole when the second drive pulse signal is applied to the coil and the second target value is defined as xcex42, the air gap changing step changes the air gap so as to meet at least one of a condition of xcex412+xcex422xe2x89xa6K1 and a condition of xcex41xc3x97xcex42 less than 0, xcex41xe2x89xa6K2, and xcex42xe2x89xa6K3 where K1, K2, and K3 are preselected target values, respectively.
According to the fifth aspect of the invention, there is provided a method of adjusting a fuel injection characteristic of a fuel injector which is designed to inject fuel into an engine and which includes: (a) nozzle having formed therein a spray hole from which fuel is sprayed; (b) a nozzle valve selectively opening and closing the spray hole; (c) an injector body supporting therein the nozzle valve slidably, the injector body having formed therein a fuel sump supplied with the fuel from an inlet formed in the injector body to produce fuel pressure urging the nozzle valve in a spray hole-opening direction, a pressure chamber supplied with the fuel from the inlet to produce fuel pressure urging the nozzle valve in a spray hole-closing direction, and a valve hole establishing fluid communication between the pressure chamber and a drain port formed in the injector body; (d) a control valve selectively opening and closing the valve hole formed in the injector body; (e) an urging mechanism disposed within an urging mechanism mount chamber formed in the injector body, the urging mechanism working to produce an urging pressure which urges the control valve in a valve hole-closing direction for closing the valve hole to block the fluid communication between the pressure chamber and the drain port; and (f) a control valve moving mechanism made up of a stationary portion and a movable portion, the stationary portion including a stator and a coil wound around the stator, the movable portion including an armature which is connected fixedly to the control valve and spaced from the stator through an air gap, the coil being energized electrically to produce an attractive force through the stator for attracting the armature to move the control valve in a valve hole-opening direction, thereby opening the valve hole to establish the fluid communication between the pressure chamber and the drain port so that the fuel pressure in the pressure chamber is decreased to move the nozzle valve so as to open the spray hole. The method comprises: (a) a first step of changing the urging pressure produced by the urging mechanism while supplying a test liquid to the fuel injector from the inlet and applying a drive pulse signal to the coil of the control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole so as to have an injection lag time fall in a target range and (b) a second step of changing the air gap between the stator and the armature while supplying a test liquid to the fuel injector from the inlet and applying a drive pulse signal to the coil of the control valve moving mechanism to energize the coil for spraying the test liquid from the spray hole so as to have a quantity of the test liquid sprayed from the spray hole fall in a target range.
In the preferred mode of the invention, the test liquid is supplied at a given pressure level lower than half a maximum pressure of the fuel which is supplied to the pressure chamber when the fuel injector is actually used to inject the fuel into the engine in each of the first and second steps.
The test liquid may alternatively be supplied at a given pressure level higher than half a maximum pressure of the fuel which is supplied to the pressure chamber when the fuel injector is actually used to inject the fuel into the engine in each of the steps.
Each of the first and second steps applies first and second drive pulse signal having different widths alternately to the coil of the control valve moving mechanism.
In the second step, at least one of the first and second drive pulse signals has the width greater than a width required for moving the nozzle valve up to a level where a maximum rate of spraying of the test liquid from the spray hole is reached.
If target quantities of the test liquid sprayed from the spray hole when the first and second drive pulse signals are applied to the coil of the control valve moving mechanism are defined as a first and a second target value, respectively, a difference between a quantity of the test liquid sprayed from the spray hole when the first drive pulse signal is applied to the coil and the first target value is defined as xcex41, a difference between a quantity of the test liquid sprayed from the spray hole when the second drive pulse signal is applied to the coil and the second target value is defined as xcex42, the air gap changing step changes the air gap so as to meet at least one of a condition of xcex412+xcex422xe2x89xa6K1 and a condition of xcex41xc3x97xcex42 less than 0, xcex41xe2x89xa6K2, and xcex42xe2x89xa6K3 where K1, K2, and K3 are preselected target values, respectively.